The invention relates to the field of telecommunications, in particular the control of access to Multicast IP streams.
In the Multicast IP broadcasting technique, the Multicast IP packets are broadcast using a particular recipient IP address, termed the Multicast address.
A Multicast stream is characterized by its source address S and by its group address G, each Multicast stream being able therefore to be represented by a unique pair (S, G). Two distinct Multicast streams can thus have the same source address S or the same group address G.
The particular feature of Multicast IP streams pertains essentially to the fact that the data supporting these streams are transmitted to the requesting terminal equipment, for example an audio-visual decoder, on the latter's request transmitted over the IP network.
The request to receive, or to stop receiving a Multicast stream is made according to the IGMP protocol, standing for Internet Group Management Protocol, defined at the IETF by recommendations RFC 1112, RFC 2236 and RFC 3376 or according to the MLD protocol, standing for Multicast Listener Discovery, defined by recommendations RFC 2710, RFC 3810.
On receipt of a reception request message, a message of the “Membership report” type, specifying the desired broadcasting source address, the first item of telecommunication equipment of the IP network capable of interpreting this request message transmits the corresponding Multicast data stream to the place from which this request message originates.
A Multicast stream broadcasting request message can also pertain to a set of sources for a given group G, the Multicast stream then being designated (*, G) and then corresponding to a sum of the streams sent by the various sources to this same group.
In the context of Multicast stream broadcasting and of the present application, the expression collection equipment denotes the network equipment handling a user's IGMP/MLD request message, so as to dispatch the corresponding Multicast data stream to said user.
At the present time, the Multicast broadcasting request message transmission protocols, of IGMP type, do not define any procedure for authenticating or authorizing a requesting user to ask for the transmission of a networked Multicast stream.
With this aim attempts have been proposed at the IETF suggesting that the aforesaid request messages be modified with the aim of trunking authentication information to an authentication/authorization platform. Successful authentication and authorization allows consideration of the requesting user's request message by the collection equipment.
The aforesaid proposal, ultimately shelved, poses the following problems:                major impact on the existing Multicast stream management protocols, because of the addition of authentication layers on the network access equipment and on the terminal equipment of the user;        need for access to an authorization platform with each Multicast stream request message transmitted by a user, a process which may appreciably increase the Multicast stream reception time in the case of Multicast broadcasting of TV programs on high-speed line of ADSL type for example.        
Another authorization approach has furthermore been proposed. According to the latter, with the aim of determining the right of a user to request the broadcasting of a determined Multicast stream, the terminal of the requesting user seeks this authorization from a specific authorization platform connected to the IP network. On receipt of the authorization request, the authorization platform returns an acceptance or a rejection of the authorization, according to the user's rights to receive the requested Multicast stream. On receipt of the accepted authorization, the user's terminal then sends the network a Multicast broadcasting request message, of the IGMP request type, so as to receive the corresponding Multicast stream.
The latter solution exhibits the following drawbacks:                need for access to an authorization platform with each message requesting broadcasting of the Multicast streams, and this may, as in the case of the previous proposal, appreciably increase the Multicast stream reception time in the case of Multicast broadcasting of a TV program on high-speed line of ADSL type;        security problem in the case where the user's terminal is modified so as to dispatch a Multicast broadcasting request message of IGMP type to the IP network without prior request of the rights to the authorization platform.        